Product having ultra high molecular weight plastic parts

ABSTRACT

A method of making a UHMWPE body combined with a bolt, a cap screw, a reinforcing member uses a compression molding machine equipped with a male and female mold set. Particulate UHMWPE dispensed into the cavity of the female mold surrounds the head of the bolt and screw and reinforcing member. Pressure and heat applied to the particulate UHMWPE molecularly bonds the UHMWPE to the bolt, screw, and reinforcing member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 09/535,691filed Mar. 27, 2000 now U.S. Pat. No. 6,475,094. application Ser. No.09/535,691 is a continuation-in-part of U.S. application Ser. No.29/098,315 filed Dec. 28, 1998, now U.S. Pat. No. Des. 426,146.

FIELD OF THE INVENTION

The invention relates to the art of pressure molding ultra highmolecular weight polyethylene (UHMWPE) to molecularly bond the UHMWPE toan article, such as a bolt, screw, plate, and reinforcing member.

BACKGROUND OF THE INVENTION

Ultra high molecular weight polyethylene, herein identified as UHMWPE,is a thermoplastic having advantageous characteristics including highabrasion resistance, low coefficient of friction and exceptionaltoughness. UHMWPE is used in a number of applications in variousindustries which require abrasion resistant and low coefficient parts.The average molecular weight of UHMWPE is from 4 to 5 million. Theplastic polymer is made up of long branch free chains, and whencompression molded, gives a material of impact strengths at roomtemperature greater than other thermoplastics. The structure of UHMWPEmakes it highly resistant to repeated stress, impact and abrasion. Theuse of UHMWPE is limited due to difficulties in its processing. The highmelt viscosity of UHMWPE limits its processing to presses and screw orram extruders. The formed pieces are machined to desired shapes.Examples of processes for molding UHMWPE are disclosed in U.S. Pat. Nos.2,400,094; 3,847,888; 3,975,481 and 5,453,234.

SUMMARY OF THE INVENTION

The invention comprises a method for making solid articles by andmolecularly bonding to metal and other materials and the completedarticles, such as a bolt having a UHMWPE cap, a socket having an UHMWPEjacket, and an UHMWPE product having a reinforcing member encapsulatedwithin the product. The method for making UHMWPE articles uses acompression molding machine equipped with a male and female moldassembly. The female mold has at least one cavity having the size andshape of the completed UHMWPE article. The male mold has a plunger thatfits into the cavity to apply substantial pressure to particulate orpowdered UHMWPE located in the cavity when the female mold is movedrelative to the male mold. The female cavity is open to a bolt retainingopening used to position the head of the bolt in the cavity. Theparticulate UHMWPE is subjected to a large compression force to purgethe particulate UHMWPE of air and force UHMWPE under the head of thebolt and densified the UHMWPE around the head of the bolt. Analternative female mold has a boss on the bottom wall of the cavity foraccommodating the socket of a socket head cap screw. A collar of UHMWPEis molecularly bonded to the head of the cap screw. A reinforcingmember, such as a metal plate, fabric, or glass fibers, is incorporatedin the UHMWPE by compressing particulate UHMWPE about the reinforcingmember and molecularly bonding the UHMWPE to the reinforcing member. Thecompressed particulate UHMWPE is heated to a temperature of between 250and 350 degrees F. to molecularly bond the UHMWPE to the part, such asthe head of the bolt, socket, and reinforcing member located in the moldcavity. The male and female molds are heated. The heat is transferred bythe mold to the compressed UHMWPE and sustained for a time to ensurethat the UHMWPE is totally sintered and molecularly bonded to thearticle located in the mold. The pressure on the heated UHMWPE ismaintained during the heating process. Upon completion of the heatingprocess the mold and UHMWPE is allowed to cool. A cooling liquid is usedto enhance the cooling rate of the UHMWPE and article. The pressure onthe UHMWPE is maintained during the cooling duration. The cooledcombined UHMWPE and article is removed from the female mold by releasingthe pressure on the UHMWPE and retracting the cavity from the plunger ofthe male mold. Air under pressure may be used to separate the UHMWPE andarticle from the female mold.

The invention includes the combined UHMWPE and article, such as the headof a bolt, a socket, a cap screw, and a reinforcing member. The bolt hasa head enclosed within a UHMWPE cap or body with the UHMWPE molecularlybonded to the top, side and bottom surfaces of the head of the bolt. Thesocket is a hand tool having a cylindrical body. A UHMWPE jacket ismolecularly bonded to the outside of the cylindrical body. The cap screwhas a head having a socket in its outer end and an outer surface. Acollar of UHMWPE is molecularly bonded to the outer surface and end ofthe head. The reinforcing member, such as a metal plate, metal member,fabric, fiber member or a glass fibers, is located within a body ofUHMWPE with the UHMWPE bonded to the reinforcing member to increase thestrength of the body of UHMWPE.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an elevator bolt having a head with aUHMWPE cap;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is an end elevational view of the left or outer end thereof;

FIG. 5 is an end elevational view of the right or inner end thereof;

FIG. 6 is a sectional view taken along the line 6—6 of FIG. 2;

FIG. 7 is a perspective view of a modification of the elevator bolt ofFIG. 1 having a head with a UHMWPE cap;

FIG. 8 is a side elevational view of FIG. 7;

FIG. 9 is a top plan view of FIG. 7;

FIG. 10 is an end elevational view of the left end of FIG. 7;

FIG. 11 is an end elevational view of the right end of FIG. 7;

FIG. 12 is a sectional view taken along the line 12—12 of FIG. 8;

FIG. 13 is a perspective view of UHMWPE combine skid show;

FIG. 14 is a top plan view of FIG. 13;

FIG. 15 is a side elevational view of FIG. 13;

FIG. 16 is a front elevational view of FIG. 13;

FIG. 17 is a rear elevational view of FIG. 13;

FIG. 18 is a bottom plan view of FIG. 13;

FIG. 19 is a top plan view of a portion of the whole of FIG. 13 having ahead bocated in the body of UHMWPE;

FIG. 20 is a front elevational view of FIG. 19;

FIG. 21 is a sectional view taken along the line 21—21 of FIG. 19;

FIG. 22 is a sectional view taken along the line 22—22 of FIG. 21;

FIG. 23 is a perspective view of a socket tool having a jacket of ultrahigh molecular UHMWPE;

FIG. 24 is a side elevational view of FIG. 23;

FIG. 25 is a top plan view of FIG. 24;

FIG. 26 is a bottom plan view of FIG. 24;

FIG. 27 is an enlarged sectional view taken along line 27—27 of FIG. 25;

FIG. 28 is a perspective view of a first UHMWPE member;

FIG. 29 is an enlarged cross sectional view taken along line 29—29 ofFIG. 28;

FIG. 30 is a top plan view, partly sectional, of the member of FIG. 28;

FIG. 31 is a perspective view of a second UHMWPE member;

FIG. 32 is an enlarged cross sectional view taken along the line 32-32of FIG. 31;

FIG. 33 is a top plan view, partly sectional, of the member of FIG. 31;

FIG. 34 is a front elevational view of a UHMWPE molding machine having aUHMWPE compression mold;

FIG. 35 is a sectional view of a portion of the mold shown in FIG. 34with a bolt positioned in the mold;

FIG. 36 is a sectional view similar to FIG. 35 with particulate UHMWPElocated in the mold;

FIG. 37 is a sectional view similar to FIG. 36 with UHMWPE plasticcompressed about the head of the bolt;

FIG. 38 is a sectional view of a portion of a mold similar to FIG. 35with a bolt of FIGS. 21 and 22 positioned in the mold;

FIG. 39 is a sectional view similar to FIG. 38 with particulate UHMWPElocated in the mold;

FIG. 40 is a sectional view similar to FIG. 39 with particulate UHMWPEcompressed about the head of the bolt;

FIG. 41 is an exploded sectional view of a mold for a socket head capscrew;

FIG. 42 is a sectional view of the mold of FIG. 41 with particulateUHMWPE plastic located in the mold;

FIG. 43 is a sectional view similar to FIG. 41 with UHMWPE plasticcompressed about the head of the cap screw;

FIG. 44 is a top plan view of the cap screw with UHMWPE ring joined tothe head of the cap screw;

FIG. 45 is a perspective view of a cap screw having a head with a UHMWPEcap;

FIG. 46 is a side elevational view of FIG. 45;

FIG. 47 is a top plan view of FIG. 45;

FIG. 48 is a sectional view taken along line 48—48 of FIG. 47;

FIG. 49 is a top plan view of FIG. 45;

FIG. 50 is a bottom plan view of FIG. 45;

FIG. 51 is a perspective view of a combined metal and UHMWPE plate;

FIG. 52 is a sectional view taken along line 52—52 of FIG. 51;

FIG. 53 is a transversely sectioned top plan view of FIG. 51;

FIG. 54 is a bottom plan view of the plate of FIG. 51 bent to alongitudinal channel shape; and

FIG. 55 is a sectional view taken along line 55—55 of FIG. 54.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIGS. 1 to 6, an elevator bolt 40 has a cylindrical body orstem 41 with external helical threads for accommodating a nut (notshown). Body 41 is joined a square neck 42 adapted to fit into a squarehole to prevent rotation of bolt 40 when used with elevator paddles.Neck 42 is connected to a circular head 43 having a flat top surface andan outwardly tapered inner surface. A cap of UHMWPE indicated generallyat 44 surrounds head 43. The plastic is a high density polyethylenehaving a very high molecular weight, herein identified a UHMWPE,characterized as having high abrasion resistance, low coefficient offriction and exceptional toughness. Other plastic materials, such asnylon, mylatron, acetel, and phenolis, can be used to mold cap 44 aroundhead 43. UHMWPE is preferred for uses of bolt 40 that require highabrasion resistance properties. Cap 44 has circular top 46, acylindrical side wall 47 and an inwardly directed annular lip 48. Top 46has a flat outer circular surface parallel to the flat top surface ofhead 43 and a uniform thickness over the entire top of head 43. Sidewall 47 extended around the outer peripheral edge of head 43 is joinedto lip 48. Top 46, side wall 47 and lip 48 are molecularly attached toor bonded to the adjacent surfaces of head 43. The thickness of theUHMWPE can be increased to molecularly bond the UHMWPE to the neck 42 toassist in preventing rotation of the head 43 relative to cap 44.

A modification of the elevator bolt indicated generally at 49 shown inFIGS. 7 to 11, have threaded body or stem 51, a cylindrical neck 52, anda cylindrical head 53. Cap 54 has a flat top 56 joined to an annularside wall 57 that surrounds the outer peripheral edge of head 53. Anannular lip 58 joined to side wall 57 extends under head 53. Top 56,side wall 57 and lip 58 are molecularly attached to or bonded to theadjacent surfaces of head 53.

The heads 43 and 53 of bolts 40 and 49 have circular or round withoutwardly tapered bottom surfaces. Bolts having heads with other shapes,such as square, hexagonal, screw slot, and carriage heads, can beprovided with UHMWPE caps. The shape of caps 44 and 54 are flat andcylindrical. Caps having other shapes, such as square, oval, rectangularand triangular, can be molecularly attached to the heads of the bolts.

Referring to FIGS. 13 to 22, a UHMWPE member 59, shown as motor supportand skid shoe, is attached to a bolt 60 and 61 extended downwardly fromthe bottom of member 59. A reinforcing sheet member 92, such as fabric,is located within UHMWPE member 59 to increase its bending strength.Bolts 60 and 61 are identical. The following description is limited tobolt 61. Bolt 61 has a threaded body or stem 62 joined to a circularhead 63. Head 63 located below the top or outer surface of member 59does not interrupt the flat, smooth, and abrasion resistant propertiesof member 59. As shown in FIGS. 21 and 22 head 63 has downwardlydirected extensions or bosses 64, 65, 66 and 67 located around body 62and projected toward bottom surface 68 of body 59. Member 59 can haveother shapes, such as round, cylindrical, oval, arcuate and triangularand support a plurality of bolts with heads embodied in the UHMWPEmember. Member 59 has an elongated curved top surface 200 extended froma front transverse lip 201 to a rear L-shaped flange 202. The bottom ofmember 59 has shoulder or stepped portion 203 having UHMWPE material foranchoring bolts 60 and 61. The head 63, projections 64-67 and a portionof body adjacent head 63 are molecularly attached to UHMWPE member 59.The process of making the UHMWPE member 59 is shown in FIGS. 38 to 40.

A socket tool 69, shown in FIGS. 23 to 27 has a UHMWPE jacket 79. Tool69 has a metal cylindrical body 71 having square hole 72 open to asocket cavity 73. Cavity 73 has a cross sectional area larger than thecross sectional area of hole 72. Twelve V-shaped ridges 75circumferentially located around cavity are adapted to grip the squareand hexagonal heads of nuts and bolts. The inside of cavity 73 can haveother shapes to accommodate specific shapes of the heads of nuts andbolts. The size of cavity 73 can vary to fit different sizes of theheads of bolt and nuts. Body 71 has a cylindrical outside wall 74, aflat top wall 76, and an annular flat bottom wall 77. Top wall 76surrounds the open end of square hole 72. Bottom wall 77 surroundsinwardly tapered portions 78 of the V-shaped ridges 75 which aid ininserting tool 69 on a nut or head of a bolt. UHMWPE jacket 79 has sidewall 81 surrounding cylindrical wall 74 of body 71, on annular top wall82 located on top wall 76 of body 71 and a bottom wall 84 coveringbottom wall 77 of body 71. Circular chambers or tapered surfaces 83 and86 are located at opposite ends of side wall 81. The side wall 81, topend wall 82, and bottom end wall 84 are molecularly attached or bondedto adjacent walls 74, 76 and 77 of body 71. Jacket 79 having lowcoefficient of friction properties does not mar, scuff, abrade norscrape recessed surfaces surrounding the heads of bolts and nuts. Anexample of nuts located in pockets having recessed surfaces are lug nutsused to attach the wheels of automobiles to brake drums. Ratchetwrenches, air wrenches, and turning tools having square drive membersare used with socket tool 79 to turn nuts and heads of bolts. The sockettool having an UHMWPE jacket can be joined to the end of a tire ironused to remove and attach lug nuts from threaded studs that hold avehicle wheel.

Proceeding to FIGS. 28 to 30, there is shown a UHMWPE member 89illustrated as a flat plate having a body 88 with flat upper and lowersurfaces 89 and 91. A mat or layer of reinforcing material 92 isencapsulated within body 88 to increase the bending strength of member89. The reinforcing material can be a fabric, glass fibers, plasticfibers, a sheet of metal screen, a plastic mesh member, canvas, cloth,or a metal sheet or plate. The layer of material 92 is located along themiddle of body 88 with generally equal amounts of UHMWPE above and belowthe layer of material 92. The opposite side edges of the layer ofmaterial 92 can be inwardly from the opposite sides of body 88 and alongthe length of body 88. The UHMWPE is molecularly attached or bonded tothe opposite sides of the layer of material 92. The layer of material 92reduces stresses in body 88. Body 88 can have shapes other than a flatplate, such as a U or horseshoe shape or the shapes of skis, snowboards, air boat pontoons, dock fenders and vehicle parts. Thereinforcing material bonded within the UHMWPE increases the bendingstrength of the plastic and inhibits the bending strength of the plasticand inhibits sagging and drooping of the body of plastic when subjectedto the weight of a heavy object, such as an internal combustion engine.The UHMWPE also absorbs vibrations and sounds.

As shown in FIGS. 31 to 33, a UHMWPE article or member 93, shown as aplate, has a body 94 with flat upper and lower surfaces 96 and 97. Body94 can have a curved or an arcuate shape. A reinforcing metal plate 98having a plurality of holes 99 is embedded within body 94 to increasethe bending strength of body 94. As shown in FIGS. 26, plate 98 islocated in the middle section of body 94 with about equal thickness ofplastic above and below plate 98. Plate 98 can be located adjacent oneof the surfaces 96 or 97 of body 94. A second plate (not shown) can beincorporated within body 94. One plate can be located adjacent surface96 and the other plates located adjacent surface 97. The member 93 canbe bent or curved after the plate 98 has been bonded to the UHMWPE.

The method of making the UHMWPE article having a reinforcing member suchas members 92 and 98, uses a mold having a cavity with a shape thatdefines the shape and size of the article. A plunger is forced into thecavity to compress the UHMWPE. A first layer of particulate UHMWPE isdeposited into the cavity. The reinforcing member is placed in thecavity on top of the first layer of UHMWPE. The reinforcing member isthen covered with a second layer of particulate UHMWPE by depositingadditional UHMWPE into the cavity. The particulate UHMWPE is a powderedUHMWPE having an average particle size between 100 to 400 μm. Theplunger is used to compress the particulate UHMWPE to increase thedensity and cohesion of the particulate UHMWPE. The compression of theUHMWPE also expells air from the particulate plastic. An example of acompression molding machine is shown in FIG. 34. The layers ofparticulate UHMWPE and reinforcing member is subjected to a pressure ofabout 1500 to 6000 psi. Other pressures can be applied to the layers ofparticulate UHMWPE as required by the size and geometry of the moldedarticle. The pressure is adjusted to ensure substantially uniformpressure on the particulate UHMWPE located in the female mold cavity andpenetration of the UHMWPE into the reinforcing material. The compressedlayers of particulate UHMWPE are heated to a temperature in the range of250 to 350 degrees F. The pressure on the layers of UHMWPE is maintainedduring the heating of the UHMWPE and for a duration sufficient to sinterthe UHMWPE and molecularly attach the UHMWPE to the reinforcing member.The UHMWPE is then cooled to a temperature below the melting temperatureof UHMWPE with the pressure material on the UHMWPE. The duration ofcooling of the UHMWPE is adjusted to ensure complete cooling of all ofthe UHMWPE. The cooled UHMWPE is removed from the mold cavity as acompleted article.

A compression molding machine 100, shown in FIG. 34, is used in theprocess of making a UHMWPE cap on the head of a bolt and a jacket on acylindrical member. Compression molding machines are also used to makeUHMWPE parts reinforced with materials and metals. Machine 100 has abase 101 enclosing a hydraulic cylinder, a pump, and controls foroperating the machine. A bed 102 mounted on cylindrical rods 106 and 107supports a table 103. A cross head 104 is attached to the upper ends ofrods 106 and 107. A mold assembly, indicated generally at 108, has afemale member 109 mounted on table 103 and male member 110 mounted oncross head 104 above female member 109. An upright cylinder 111 mountedon base 101 is used to move bed 102 toward and away from the cross head104 to operate mold assembly 108.

Mold female member 109 has a number of cavities 112 and bolt retainingopenings or holes 113 for holding bolts. One cavity 112 and boltretaining hole 113 is shown in FIG. 35. The remaining cavities and holeshave the same shapes as cavity 112 and hole 113. Cavity 112 has acylindrical shape and a flat bottom. Mold 109 has an annular shoulder orwall 114 at the bottom of cavity 112 surrounding bolt retaining hole113. Hole 113 has a square cross section to accommodate the square neck42 of bolt 40 and hold bolt 40 in an upright position. The head 43 ofbolt 40 is located in cavity 112. The inside portion of the bottom ofhead 43 rests on the wall 114 around hole 113, when neck 42 is in hole113. Mold heating rods or elements 116 and 117 located in member 109adjacent cavities 112 heat member 109 and particulate UHMWPE located incavities 112. Heating elements are electric heating members connected toa source of electric power. Other types of heating devices can be usedto heat mold members 109 and 110. Member 109 has passages 120 and 125for accommodating cooling liquids to cool mold member 109.

Mold member 110 has a number of plungers 118 operable to compressparticulate UHMWPE located in cavities 112. Plungers 118 are downwardlydirected cylindrical members having diameters slightly less than thediameter of the cylindrical cavities 112. Plungers 118 have a closesliding fit with the cylindrical walls of member 109. Electric heatingelements or rods 119 and 121 located in member 110 adjacent each plunger118 are operable to transfer heat to plungers 118 and UHMWPE located incavities 112.

As shown in FIGS. 35 to 37 a UHMWPE cap is molded on bolt head 43. Bolt40 is inserted into cavity 112 to place neck 42 in the square hole 113.Neck 42 located in hole 113 retains bolt in an upright position with theaxis of bolt 40 aligned with the axis of cavity 112. The bottom of head43 adjacent neck 42 rests on shoulder 114. The outer peripheral edge orrim of bolt 40 is spaced inwardly of the cylindrical wall of cavity 112and above shoulder 114. As shown in FIG. 36, particulate UHMWPE 124 isdeposited in cavity 112 around and above head 43. The thickness of thetop of the cap 44 on head 43 is related to the amount of particulateUHMWPE placed in cavity 112. The volume of particulate UHMWPE is about 2to 2.5 times the volume of the part or cap manufactured from it. theparticulate UHMWPE is a powdered linear polyethylene having an averageparticle size from 100 to 400 μm. The particulate UHMWPE in cavity 112is compressed around head 43, as shown in FIG. 31, by moving plunger 118into cavity 112. Cylinder 111 is expanded to move bed 102 and cross head104 toward each other as shown by arrows 122 and 123 to move plunger 118into cavity 112. The particulate UHMWPE is subjected to a pressure ofabout 1500 to 6000 psi. Other pressures can be used to compress theparticulate UHMWPE. The pressure applied to the particulate UHMWPEdepends on the amount of UHMWPE to be processed and the geometry of themolded part. Higher pressures are used for larger amounts of particulateUHMWPE and for shapes which have different wall thicknesses. Thecompression of the particulate UHMWPE increases the density and cohesionof the particulates and expels gases from the particulate mass. Thecompressed UHMWPE is heated to a temperature in the range of 275 to 350degrees F. with heating elements 116, 117, 119 and 121. The pressure onthe compressed UHMWPE is maintained during the heating of the male andfemale mold members 109 and 110 and the transfer of heat to thecompressed UHMWPE. The heat subjected to the compressed UHMWPE is attemperatures above the crystalline melting point of UHMWPE for a timesufficient to sinter the UHMWPE and molecularly attach the UHMWPE tohead 43 of bolt 40. The temperature is preferably between 300 to 320degrees F. The time that the UHMWPE is subjected to heat is a durationthat ensures that all parts of the compressed UHMWPE is within thesintering temperature ranges of the UHMWPE in cavity 112. The increasein pressure of the heated UHMWPE in addition to the pressure appliedwith plunger 118 increases the densification of the UHMWPE and molecularattachment of the UHMWPE to all areas of head 43 located in the cavity112. The annular lip 48 located under head 43 is firmly attached to thebottom of head 43. The mold assembly 108 is kept in its closed positionapplying pressure of the UHMWPE as it is cooled to externalenvironmental temperature. Cooling occurs by heat transfer tosurrounding metal members 109 and 111 and air. Coolants, such as air orwater in the male and female members 109 and 110 flow through passages120 and 125 to increase the rate of cooling of the UHMWPE in the moldcavity 112. The cooling time depends on the size of the molded part andthe method used to transfer heat from the male and female members 109and 110. The cooling duration is adjusted to allow all the UHMWPE toattain a generally uniform temperature below the melting temperature ofUHMWPE. The pressure on the UHMWPE is removed after the cooling iscompleted. The mold assembly 109 is expanded to withdraw plunger 118from cavity 112. The UHMWPE cap 44 attached to head 43 of bolt 40 isthen removed from female member 109. Air under pressure in opening 113can be used to expel bolt 40 out of cavity 112.

Referring to FIGS. 38 to 40, there is shown a female mold member 126 ofa mold assembly including a male member having a plunger 134. Member 126has a cavity 127 and a downwardly extend bolt retaining opening or hole128 open to the bottom of cavity 127. Cavity 127 has the shape of member59. The shape and size of cavity 127 conforms to the shape of thecompleted part, such as a motor support or plate. Opening has a diameterslightly less than the diameter of body 62 of bolt 61. Body 62 fits intoopening 128 and engages the cylindrical wall 130 of member 126surrounding opening 128 to retain bolt 61 in an upright position andstabilize bolt 61 on mold member 126.

Mold member 126 has a flat annular wall or shoulder 132 at the bottom ofcavity 127 surrounding opening 128. Heating elements or rods 129 and 131are located in member 126 adjacent wall 132. Heating elements 129 and131 are electric heating members coupled to a source of electric poweroperable to heat member 126 which conducts heat to particulate UHMWPElocated in cavity 127. Other types of heating devices can be used toheat member 126 or subject particulate UHMWPE to a selected temperaturerange.

A UHMWPE member 59 is attached to head 63 and projections 64-67.Additional bolts, such as bolts, 60 and 61, can be attached to member 59currently with bolt 61. Mold member 126 can have additional boltretaining openings for accommodating additional bolts. The bolt 61 isplaced in cavity 127 with body 62 located in opening 128. Projections64-67 have lower ends that engage wall 132 and space the bottom of head63 above wall 132. As shown in FIG. 39, particulate UHMWPE 133 isdeposited in cavity 127 above and around head 63. The selected thicknessof plate 59 or size and shape of the completed object determines theamount of particulate UHMWPE placed in cavity 127. The average particlesize of the particulate UHMWPE is in the range described herein withreference to particulate UHMWPE 124. Female member 126, shown in FIG.40, moves up into plunger 134 to subject particulate UHMWPE to pressureto increase the density of the particles and reduce gas and voids in themass of particulate UHMWPE. The compressed particulate UHMWPE is heatedunder pressure with heat conducted from heating elements 129 and 131 andheating elements in the male member of the mold assembly. The pressure,heating temperature range, cooling, and removal of completed plate isthe same as herein described with reference to FIGS. 35 to 37.

A mold assembly 137 for a socket head cap screw 144 shown in FIGS. 41 to43, has a female member 138 and a male member 150 operable to attach aUHMWPE sleeve or ring on the head of a screw 144. Member 138 has aninside cylindrical wall 139 and a flat bottom wall 141 surrounding acavity 142. A hexagonal boss or short shaft 143 secured to the center ofbottom wall 141 retains cap screw 144 in an upright position in cavity142. The axis of cap screw 144 coincides with the upright axis of cavity142. Cap screw 144 has a threaded body or stem 146 joined to acylindrical head 147 having a hexagonal socket or recess 148. Socket 148fits over boss 143 to hold cap screw 144 on member 138. Boss 143 extendsupwardly from a cylindrical member 145 joined to bottom wall 141. Member145 spaces the outer end of head 147 above bottom wall 141. A tubularmember or sleeve 149 surrounds the entire length of body 146, as shownin FIGS. 42 and 43. The male member 150 is a tubular cylindrical plungerhaving an axial center passage or bore 151 having a size to slidably fitover sleeve 146. The inside diameter of sleeve 146 slidably accommodatesbody 146 of cap screw 144 whereby plunger 151 telescopes over sleeve 149to maintain cap screw 144 in its upright position during compression ofparticulate UHMWPE 152 in cavity 152 around the sides and top of head147.

The process of molecularly attaching a UHMWPE collar or ring 152, asshown in FIG. 43, on cap screw 147 is commenced by placing head 147 ofcap screw 144 on hexagonal boss 143 to locate cap screw 144 in cavity142 with the outer end of head spaced above bottom wall 141. Sleeve 149is placed over body 146 of cap screw 144. As shown in FIG. 42,particulate UHMWPE is deposited in cavity around the sides and outer endof head 147 and sleeve 149. The amount of particulate UHMWPE depositedin cavity 142 is dependent upon the size and shape of the collar bondedto head 147. Plunger 151 is moved down into cavity 142 to apply pressureto the particulate UHMWPE 152. Heating elements 154 and 156 areoperational to heat member 13.8 which transfers heat to the compressedUHMWPE. The pressure on the UHMWPE is maintained during the heatingstage. After the heating cycle, the mold 138, compressed UHMWPE and capscrew are cooled with a cold liquid flowing through passages 157 and158. The duration of the cooling cycle is adjusted to insure that allthe UHMWPE is cooled to a generally uniform temperature below themelting temperature of UHMWPE. The cap screw joined to the UHMWPE isthen removed from the mold. The heating temperature range, cooling, andremoval of the completed combined cap screw and UHMWPE collar is thesame as herein described with reference to FIGS. 35 to 37.

A modification of the cap screw 249 with a UHMWPE cap 254 is shown inFIGS. 45 to 50. Cap screw 249 has a threaded body or stem 252 and a coneshaped head 252 with a hexagonal socket 253. A cap 254 comprising UHMWPEis molecularly bonded to head 252 and an annular washer 259 surroundingthe head 252. Washer 259 engages the tapered inside wall of head andprovides a large annular surface to anchor the UHMWPE and prevent cap254 from being pulled off head 252. Cap 254 has a flat top surface 256,a cylindrical side wall 257 and an inside wall 258. Wall 258 is locatedbelow washer 259. The molding process shown in FIGS. 41 to 43 is used tomold the UHMWPE cap 254 on head 252 and washer 259.

A combined metal and UHMWPE plate 300, shown in FIGS. 51 to 55, has ametal sheet or layer 301 and a generally flat body 304 of UHMWPE joinedto metal sheet 301. Sheet 301 smooth metal member having uniformthickness with generally flat upper and lower surfaces 302 and 303.Sheet 301 can be steel, aluminum or other metals. A rubber-like chemicallocking adhesive layer 306 located between metal sheet 301 and UHMWPEbody 304 joins sheet 301 to body 304.

The combined metal and UHMWPE plate 300 is made by cleaning the surface303 of metal sheet 301 with sandblasting the entire surface 303 andetching surface 303 with a liquid etching chemical. The adhesive layer306 is applied to the etched surface 303. A pressure molding machine, asshown in FIG. 34, equipped with a male and female mold assembly is usedto molecularly bond metal surface 303 to layer 306 and UHMWPE to layer306. The mold assembly has a cavity having the shape of the finishedarticle. A measured amount of powdered UHMWPE is placed in the cavity.The metal sheet 303 and layer 306 is placed on top of the powderedUHMWPE in the cavity. The powdered UHMWPE, layer 306, and flat metalsheet 301 is subjected to high pressure and heat between 250 to 350degrees F. The duration of the heating cycle is adjusted to ensure thatall the powdered UHMWPE is sintered into a solid UHMWPE body. The heatcures the adhesive 306 and bonds the metal sheet surface 303 and UHMWPEto the adhesive. The pressure on the metal sheet 301 and UHMWPE ismaintained during the heating cycle. After the heating cycle iscompleted the mold assembly is cooled to a temperture below the meltingtemperature of UHMWPE. The pressure on the metal sheet 301 and UHMWPEbody 304 is maintained during the cooling duration. The duration of thecooling cycle is also adjusted to ensure complete cooling of the UHMWPE.The mold assembly is separated and the combined metal and UHMWPE plate300 is removed from the mold assembly. As shown in FIGS. 54 and 55, thecombined metal and UHMWPE plate 300 is pressed or bent into a channelshape. The UHMWPE has longitudinal linear corners 307 and 308. The metalsheet 301 reinforces the UHMWPE body 304 along its entire length.

Modifications of the process and products of the invention may be madeby persons skilled in the art without departing from the invention asdefined in the following claims.

What is claimed is:
 1. A combined bolt and UHMWPE cap comprising: athreaded stem, a head, and a neck connecting the stem to the head, saidhead having a top surface and a bottom surface, the top surface of thehead is flat, and the bottom surface of the head tapers outwardly, and acan of UHMWPE surrounding said head and molecularly bonded to said topand bottom surfaces.
 2. A combined bolt and UHMWPE cap comprising: athreaded stem, a head, and a neck connecting the stem to the head, awasher surrounding the neck located in engagement with the head, and acap of UHMWPE surrounding the head and washer and molecularly bonded tosaid head and washer.
 3. The combined bolt and UHMWPE cap of claim 2wherein: the washer has a diameter greater than the transverse dimensionof the head.
 4. A combined bolt and UHMWPE cap comprising: a threadedstem, a head, a neck connecting the stem to the head, said neck having anon-cylindrical shape and a can of UHMWPE molecularly bonded to thehead.
 5. A combined bolt and UHMWPE body comprising: a bolt having astem and a head connected to the stem, and a body of UHMWPE molecularlybonded to the head, said head having a bottom surface and a plurality ofprojections extended downwardly from the bottom surface, said body ofUHMWPE surrounding said projections and molecularly bonded to saidbottom surface and projections.
 6. A combined bolt and UHMWPE bodycomprising: a bolt during a stem and a head connected to the stem, awasher surrounding the stem located in engagement with the head, and abody of UHMWPE surrounding the head and washer and molecularly bonded tosaid head and washer.
 7. The combined bolt of UHMWPE body of claim 6wherein: the washer has a diameter greater than the transverse dimensionof the head.
 8. A combined bolt and UHMWPE cap comprising: a threadedstem, a head connected to the stem, said head having a flat top surfaceand an outwardly tapered bottom surface, and a cap of UHMWPE surroundingthe head and molecularly bonded to said top and bottom surfaces.
 9. Thecombined bolt and UHMWPE cap of claim 8 including: a washer surroundingand located in engagement with the bottom surface of the head, said capof UHMWPE surrounding the head and washer and molecularly bonded to saidhead and washer.
 10. The combined bolt and UHMWPE cap of claim 9wherein: the head has a diameter and the washer has a diameter greaterthan the diameter of the head.
 11. A combined bolt and UHMWPE capcomprising: a threaded stem, a head having a bottom surface connected tothe stem, a washer surrounding the head located in engagement with thebottom surface of the head, and a cap of UHMWPE surrounding the head andwasher and molecularly bonded to said head and washer.
 12. The combinedbolt and UHMWPE cap of claim 11 wherein: the washer has a diametergreater than the transverse dimension of the head.